Mycobacterium is a genus of Actinobacteria, with its own family—the Mycobacteriaceae. There are more than 70 species of mycobacteria, with characteristic rod-like shapes and waxy outer coats. Tuberculosis (Mycobacterium tuberculosis) and leprosy (Hansen's disease; Mycobacterium leprae) are the best known mycobacterial diseases. Hosts may be colonized by mycobacteria without showing any adverse signs. For example, billions of people around the world have asymptomatic infections of Mycobacterium tuberculosis. 
Mycobacterial infections are notoriously difficult to treat. The organisms are hardy due to their cell wall, which is neither truly Gram negative nor Gram positive. In addition, mycobacteria are naturally resistant to various antibiotics that disrupt cell-wall biosynthesis, such as penicillin. Due to their unique cell wall, they can survive long exposure to acids, alkalis, detergents, oxidative bursts, lysis by complement, and many antibiotics. Most mycobacteria are susceptible to the antibiotics clarithromycin and rifamycin, but antibiotic-resistant strains have emerged.
Mycobacteria can be classified into several major groups for purpose of diagnosis and treatment: Mycobacterium tuberculosis complex, which can cause tuberculosis (M. tuberculosis, M. bovis, M. africanum, and M. microti); Mycobacterium leprae, which causes Hansen's disease or leprosy; and non-tuberculous mycobacteria (NTM), which can cause pulmonary disease resembling tuberculosis, lymphadenitis, skin disease, or disseminated disease.
The R-iminophenazine derivative clofazimine or CFZ ([3-(4-chloroanilino)-10-(4-chlorophenyl)-2,10-dihydro-2-(isopropylimino)-phenazine]; FIG. 1) was synthesized more than 50 years ago and found to be a strong antimycobacterial antibiotic (Barry, et al., 1957, Nature 179:1013-1015; O'Connor, et al., 1995, Drug Metab. Rev. 27:591-614; Reddy, et al., 1999, J. Antimicrob. Chemother. 43:615-623). Although able to kill most mycobacteria in vitro including Mycobacterium tuberculosis, CFZ was ineffective in animal models of tuberculosis (Barry, et al., 1957, Nature 179:1013-1015; O'Connor, et al., 1995, Drug Metab. Rev. 27:591-614; Reddy, et al., 1999, J. Antimicrob. Chemother. 43:615-623). CFZ achieved status as an antibiotic in the treatment of leprosy and is currently part of the three-drug treatment regimen approved for multibacillary disease by the World Health Organization (Reddy, et al., 1999, J. Antimicrob. Chemother. 43:615-623).
The apparent inability of most mycobacteria, including isolates of Mycobacterium tuberculosis, to develop resistance to CFZ (Reddy, et al., 1999, J. Antimicrob. Chemother. 43:615-623) has led to a resurgence of interest in the drug. Currently, new CFZ analogs are being tested for treatment of Mycobacterium avium infections associated with AIDS and for multi-drug resistant tuberculosis (Reddy, et al., 1999, J. Antimicrob. Chemother. 43:615-623; Reddy, et al., 1996, Antimicrob. Agents Chemother. 40:633-636; Sano, et al., 2004, Antimicrob. Agents Chemother. 48:2132-2139; and Van Rensburg, et al., 2000, Chemother. 46:43-48). Although CFZ has primarily antimycobacterial activity, experimental evidence suggests a broader based activity toward Gram-positive bacteria (Oliva, et al., 2004, J. Antimicrob. Chemother. 53:435-440; Van Rensburg, et al., 1992, Antimicrob. Agents Chemother. 36:2729-2735) and strains of yeast (Rhodes, et al., 1973, Biochem. Pharmacol. 22:1047-1056). Apart from its antibiotic properties, CFZ appears to have anti-inflammatory properties exhibiting the ability to suppress neutrophil and lymphocyte activity (Krajewska, et al., 1993, Int. J. Immunopharmac. 15:99-111; Zeis, et al., 1986, Int. J. Immunopharmac. 8:731-739; Sanchez, et al., 2000, Clin. Dermatol. 18:131-145; Ren, et al., 2008, PLoS ONE 3:1-11). This immunosuppressive effect currently is being explored in treatments of autoimmune disorders, including multiple sclerosis, lupus, and psoriasis (Sanchez, et al., 2000, Clin. Dermatol. 18:131-145; Ren, et al., 2008, PLoS ONE 3:1-11). Lastly, CFZ may have anticancer activity (Van Rensburg, et al., 1993, Cancer Res. 53:318-323; Durandt, et al., 2001, Int. J. Oncol. 19:579-583).
The mechanism(s) of action of CFZ has remained elusive. The drug is extremely hydrophobic (c Log P=7.5), suggesting that it functions in association with membranes (O'Connor, et al., 1995, Drug Metab. Rev. 27:591-614: Franzblau, et al., 1989, Antimicrob. Agents Chemother. 33:2004-2005). Studies have pointed to inhibition of K+ transport, but it is not clear whether inhibition results from a specific interaction(s) or is a consequence of membrane disruption (Bopape, et al., 2004, J. Antimicrob. Chemother. 53:971-974; Cholo, et al., 2006, J. Antimicrob. Chemother. 57:79-84). CFZ also is reported to bind to DNA, but the mechanism of this interaction is unclear and does not appear to be through base intercalation like other dyes that disrupt DNA function (Morrison, et al., 1976, Int. J. Lepr. 44:475-481).
The first published study on CFZ noted that it was a redox active compound and that it was reduced and oxidized within mycobacteria, likely in conjunction with respiratory chain activity (Barry, et al., 1957, Nature 179:1013-1015). Because reduced forms of dyes such as CFZ were known to produce reactive oxygen species (ROS) upon reoxidation in air, it was argued that the generation of ROS was an important aspect of the mechanism of action of the drug. In support of this argument, mycobacteria deficient in catalase activity showed a greater sensitivity to CFZ than wild type bacteria.
There is a need in the art to identify novel compounds useful in the treatment of mycobacterial infections. These compounds should be active against mycobacteria and highly developable as drugs. There is further a need for novel agents that are active against Gram-positive bacteria or yeast. There is also a need for novel anti-inflammatory agents. Such agents may be useful in treating autoimmune disorders, including for example multiple sclerosis, lupus, and psoriasis. There is further a need for novel anticancer agents. The present invention addresses these needs.